Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are placed in a feed chute and delivered to a heater assembly. Delivery of the solid ink may be accomplished using gravity or an electromechanical or mechanical mechanism or a combination of these methods. At the heater assembly, a heater plate melts the solid ink impinging on the plate into a liquid that is collected and conveyed to a print head for jetting onto a recording medium.
In known printing systems having an intermediate imaging member, the print process includes an imaging phase, a transfer phase, and an overhead phase. In ink printing systems, the imaging phase is the portion of the print process in which the ink is expelled through the piezoelectric elements comprising the print head in an image pattern onto a print drum or other intermediate imaging member. The transfer or transfer phase is the portion of the print process in which the ink image on the imaging member is transferred to the recording medium. The image transfer typically occurs by bringing a transfer roller into contact with the image member to form a transfer nip. A recording medium arrives at the nip as the imaging member rotates the image through the transfer nip. The pressure in the nip helps transfer the malleable image inks from the imaging member to the recording medium. In the overhead phase, the trailing edge of the recording medium passes out of the nip and the transfer roller is released from contacting the image member. When the image area of an image recording substrate has passed through the transfer nip, the overhead phase begins. The transfer roller may be immediately retracted from the imaging member as the trailing edge of the substrate passes through the nip, or it may continue to roll against the imaging member at a reduced force and then be retracted. The transfer roller and/or intermediate imaging member may be, but is not necessarily, heated to facilitate transfer of the image. In some printers, the transfer roller is called a fusing roller. For simplicity, the term “transfer roller” as used herein generally refers to all heated or unheated rollers used to facilitate transfer of an image to a recording media sheet or fusing the image to a sheet.
Many printers have multiple trays in which different types of recording media are stored. These different media may be different sizes of paper or polymer film recording media. These various media also have different thicknesses. As media are introduced to the transfer nip, the transfer roller climbs the lead edge of the media as the media enters the nip. Transfer of the image to the media under pressure at the nip, known as transfer or transfix, occurs nominally under uniform and constant force as the force between the transfer roller and the intermediate imaging member is regulated. The torque required for climbing the edge of a media sheet at the nip is a function of, but not limited to, the pressure of the transfer roller against the intermediate imaging member, the thickness of the media entering the nip, and the rotational speed of the intermediate imaging member. Thicker media and higher transfer roller pressures may stall the intermediate imaging member drive system with excessive drive belt slip or drive servo following error. Efforts to configure the transfer roller so it applies a single pressure to the intermediate imaging member that accommodates all the various thicknesses of media have involved tradeoffs between throughput and/or image quality/durability.